micky wrote:

Long after I ordered one for $18, it suddenly dawned on me that if it
can't play an MP3 CD, it won't be able to play an MP3 file from a
USB-connected flashdrive.

The car radio won't see a USB device, it'll see an aux level analogue
input, hopefully the $18 device acts as an MP3 player with e.g. 1/8"
jack analogue output?

Got a link?